The present invention relates to a semiconductor memory and, more particularly, a nonvolatile semiconductor memory using, as memory cells, field effect transistors each including a floating gate within a gate insulating film.
In a nonvolatile semiconductor memory such as an erasable and electrically programmable read only memory (EPROM) using field effect transistors each having a floating gate within an insulating film to program a memory cell, that is, to inject electrons into the floating gate, a program voltage (e.g. 25 V) is simultaneously applied to the gate and drain of a memory insulating gate field effect transistor. Usually, about 50 milliseconds are taken to program a single memory cell. In this case, the programming is performed every word. Accordingly, about 1.7 minutes are taken to program all the memory cells of a memory of 2048 words.times.8 bits, and about 3.4 minutes for a memory of 4096 words.times.8 bits.
In the die sort process of semiconductor memories, all the dies on a single wafer are tested as to whether all the memory cells can be programmed or not. In the case of the memory of 4096 words.times.8 bits, if 150 dies, for example, fabricated on a single wafer, the time taken for the programming test of all of the dies is 3.4 minutes.times.150=510 minutes, or 8.5 hours.
The same thing can be said for actual data programming of semiconductor memories. A long programming time is taken for programming memories word by word.